1. Field of the Invention
The present invention relates to idler mechanism and image formation apparatus having an idler mechanism. More specifically, the present invention relates to a thermal transfer printer having an idler mechanism.
2. Background Information
Types of thermal transfer printer that are known in the past include sublimation types and TA (thermo Autochrome) types. With a full-color thermal transfer printer, the printing is performed one color at a time. Accordingly, there has been known a mechanism for retracting paper that has been fed out and feeding it back out again to allow printing in multiple colors. To accomplish this, the motor is rotated in reverse, or an idler mechanism is utilized. FIG. 6 is a partial side schematic view of a standard sublimation type thermal transfer printer equipped with an idler mechanism. In this diagram, the gear teeth are indicated by dashed lines for the sake of simplicity.
A sublimation thermal transfer printer 100 includes a pickup lever 111 that moves a paper tray (not shown) up and down, a paper feed roller 112 that picks up the paper contained in the paper tray, a press roller 113 and spike roller 114 that convey paper while applying pressure, and a paper discharge roller 116 for discharging the paper.
The sublimation thermal transfer printer 100 is further equipped with various motors and gears. A feed motor 134 drives a feed gear 120a. First feed gears 120a and 120b are formed integrally and coaxially, and the first feed gear 120b meshes with a second feed gear 121a. The second feed gears 121a and 121b are formed integrally and coaxially, and the second feed gear 121b meshes with a feed roller gear 122.
The feed roller gear 122 is coupled fixedly and coaxially with the spike roller 114, such that the movement of the feed roller gear 122 is linked to that of the spike roller 114. The feed roller gear 122 meshes with a first pickup gear 127a. The first pickup gears 127a and 127b are formed integrally and coaxially, and the first pickup gear 127b meshes with a second pickup gear 128.
The second pickup gear 128 meshes with first and second pickup idler gears 129a and 129b. A spring (not shown) for generating rotational torque during swinging is inserted into the shaft of one of the first and second pickup idler gears 129a and 129b. These pickup idler gears 129a and 129b are connected by an L-shaped pickup idler arm 130 to the second pickup gear 128. The first pickup idler gear 129a meshes with a pickup roller gear 131 when the pickup idler arm 130 swings toward the pickup roller gear 131. The pickup roller gear 131 is coupled fixedly and coaxially with the paper feed roller 112, and its movement is linked to that of the paper feed roller 112. Meanwhile, the second pickup idler gear 129b meshes with a third pickup gear 132 when the pickup idler arm 130 swings toward the third pickup gear 132. In the state shown in FIG. 6, the first pickup idler gear 129a is meshed with the pickup roller gear 131.
The third pickup gear 132 meshes with the pickup roller gear 131. The pickup roller gear 131 in turn meshes with an eject roller gear 133. The eject roller gear 133 is coupled fixedly and coaxially with the paper discharge roller 116, and its movement is linked to that of the paper discharge roller 116. In this manner, the paper is shifted to the paper ejection direction (right hand side direction as viewed in FIG. 6).
An idler stopper 101 is provided coaxially with the pickup gear 127a. A protrusion 130b is formed on the pickup idler arm 130 so as to come into contact with the idler stopper 101. In the state in FIG. 6, the protrusion 130b is biased upward by the idler stopper 101, so the swinging angle of the idler arm 130 is prevented, and the first pickup idler gear 129a is meshed with the pickup roller gear 131.
FIG. 7 is a partial side see-through view of the sublimation thermal transfer printer 100 during the paper feed operation. The pickup lever 111 is driven and its distal end rises during the paper feed operation. The paper tray is lifted up by this distal end, and when the uppermost sheet of paper hits the paper feed roller 112, it is fed out by the rotation of the paper feed roller 112. At this point, the raising of the pickup lever 111 causes the idler stopper 101 to rotate clockwise, stopping its biasing of the protrusion 130b. Since the second pickup gear 128 rotates in the direction indicated by the arrow 210 during the paper feed operation, the pickup idler arm 130 is also subjected to rotational torque in the direction of the arrow 210. Therefore, the pickup idler arm 130 rotates toward the third pickup gear 132 and the second pickup idler gear 129b meshes with the third pickup gear 132.
As the third pickup gear 132 rotates in the direction of the arrow 210, the second pickup idler gear 129b rotates in the direction of the arrow 211, and the third pickup gear 132 rotates in the direction of the arrow 212. Then, the pickup roller gear 131 rotates in the direction of the arrow 213, and the paper feed roller 112 rotates in the direction of the arrow 214.
However, with the sublimation thermal transfer printer 100 shown in FIGS. 6 and 7, a spring is necessary for obtaining the oscillation torque of the idler mechanism, which makes the structure complicated. Also with such structure, a situation can occur in which neither of the first and second pickup idler gears 129a and 129b is meshed with either the pickup roller gear 131 or the third pickup gear 132.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for improved idler mechanism, image formation apparatus, and thermal transfer printer that overcome problems of the prior art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.